1. Technical Field of the Invention
The present invention relates to a liquid crystal device and a manufacturing method therefore, and an electronic apparatus comprising the liquid crystal device.
2. Description of the Related Art
Recently, liquid crystal devices have been widely used as display sections of electronic apparatuses such as cell phones, portable information terminal devices, wristwatches, etc. Such a liquid crystal device comprises a plurality of display dots arranged, for example, in a matrix form so that the voltage applied to a liquid crystal is controlled for each display dot to modulate light transmitted through the liquid crystal for each display dot, thereby displaying an image such as a character, a numerical character, a figure, or the like on the outside.
As the liquid crystal device having the above-described construction, a reflective liquid crystal device and a transmissive liquid crystal device are known according to the system for supplying light to a liquid crystal. The reflective liquid crystal device is a liquid crystal device having a structure in which a display is performed by utilizing light incident on the liquid crystal device from the observation side and then reflected by the back of the liquid crystal. On the other hand, the transmissive liquid crystal device is a liquid crystal device having a structure in which a display is performed by utilizing light from an illumination device provided on the back of the liquid crystal.
The reflective liquid crystal device does not use an illumination device such as a back light or the like, and thus consumes little electric power, and is conventionally used as the display section for various electronic apparatuses. However, the reflective liquid crystal device performs a display by utilizing external light such as natural light, illumination light, or the like, and thus has the problem of the display being difficult to be seen in dark places.
Therefore, a liquid crystal device has been proposed, in which it utilizes external light in a bright place like the reflective liquid crystal device, while it utilizes an internal light source for making the display visible in a dark place.
Namely, the liquid crystal device uses a display system including a reflective system and a transmissive system, and the display system is switched between the reflective and the transmissive display systems according to surrounding brightness, thereby permitting a clear display even in a dark environment while decreasing power consumption. In the specification of this application, this type of liquid crystal device is referred to as a “transflective liquid crystal device”.
As the transflective liquid crystal device, a liquid crystal device comprising a transflective film, i.e., a so-called half mirror, is conventionally known. This transflective film is formed by optimizing the thickness of a metal film of aluminum or the like, which is generally used as a reflecting film in the optical field, so that light is transmitted to some extent, and at the same time, light is reflected to some extent. However, a deposition technique such as mask sputtering or the like is required for forming the transflective film, complicating the process and causing the fault that variations in transmittance and reflectance are increased due to a large variation in thickness.
Therefore, in order to overcome the fault of the transflective film, a liquid crystal device has been proposed having a structure in which a light transmission slit, i.e., an aperture, is formed in a reflecting film. FIG. 6 shows a simple matrix system transflective color liquid crystal device as an example of the liquid crystal device having this structure. In the liquid crystal device 70 shown in FIG. 6, a liquid crystal 73 is held between a pair of transparent substrates 71 and 72. Also, a reflecting film 74, a color filter 75, an overcoat film 76, a silicon oxide film 77 and a segment electrode 78 are laminated in turn on the liquid crystal-side surface of the lower substrate 71. Furthermore, a common electrode 79 is formed on the liquid crystal-side surface of the upper substrate 72.
The color filter 75 formed on the lower substrate 71 comprises colorant layers 75r, 75g and 75b having different colors including red (R), green (G) and blue (B), respectively, which are arranged in a predetermined planar pattern, for example, a stripe pattern, as viewed from the direction of arrow A. The segment electrode 78 comprises a transparent conductive film of ITO (Indium Tin Oxide), and is formed in stripes, as viewed from the direction of arrow A. On the other hand, the common electrode 79 comprises a transparent conductive film of ITO (Indium Tin Oxide), and is formed in stripes perpendicular to the segment electrode 78.
The reflecting film 74 formed on the lower substrate 71 comprises a metal film of aluminum or the like, which has high reflectance. The reflecting film 74 also has a light transmission slit 80 formed for every display dot. Furthermore, polarizer plates 82a and 82b are provided on the outsides of the upper and lower substrates 71 and 72, respectively, and an illumination device 83 such as a back light is disposed on the lower side of the lower substrate 71, i.e., on the back opposite to the observation side.
When the liquid crystal display device 70 having the above construction is used in a reflective display state in a bright place, external light incident on the upper substrate 72 is transmitted through the liquid crystal 73, reflected by the surface of the reflecting film 74, again transmitted through the liquid crystal 73 and then emitted from the upper substrate 72, as shown by arrow R. On the other hand, when the liquid crystal display device 70 is used in a transmissive state in a dark place, light emitted from the illumination device 83 provided outside the lower substrate 71 is transmitted through the slits 80 of the reflecting film 74, transmitted through the liquid crystal 73 and then emitted from the upper substrate 72. The light contributes to a display in each of the display states.
In the above-described transflective liquid crystal device, a metal film of aluminum or the like is conventionally used as the reflecting film. However, a brighter screen has been demanded recently, and thus an APC alloy having higher reflectance than aluminum, i.e., a silver-palladium-copper (Ag—Pd—Cu) alloy, has been used.
However, APC has the property that it has low water resistance in the production process, and thus an APC pattern is eluted by electrical ionization, thereby causing electromigration and electrolytic corrosion (i.e., corrosion) due to the electromigration. There is thus the problem of reliability. In this way, it is difficult to use APC singly, and it has been thus proposed that ITO is laminated above or below APC to form a laminated film used as a transflective film.
FIG. 7 shows an example of a transflective color liquid crystal device having a structure in which light transmission slits are formed in a reflecting film comprising a laminated film of APC and ITO. In the liquid crystal device 60 shown in FIG. 7, a liquid crystal 63 is held between a pair of transparent substrates 61 and 62. A segment electrode 67 having a laminated structure comprising an APC film 65 having slits 64, and an ITO film 66 formed thereon is formed in stripes on the liquid crystal-side surface of the lower substrate 61, as viewed from the direction of arrow A. Furthermore, an alignment film 68 is formed on the segment electrode 67.
On the other hand, a color filter 59 comprising colorant layers 59r, 59g and 59b having R, G and B colors, an overcoat film 58, a common electrode 57 comprising an ITO film formed in stripes as viewed from the direction of arrow A, and an alignment film 56 are formed in turn on the upper substrate 62. Furthermore, polarizer plates 82a and 82b are provided on the outer surfaces of the lower and upper substrates 61 and 62, respectively, and an illumination device 83 such as a back light is disposed on the lower side of the lower substrate 61, i.e., on the back opposite to the observation side.
In the above-described construction, the laminated film comprising the APC film 65 and the ITO film 66 formed on the lower substrate 61 functions as a transflective film, and at the same time, functions as an electrode for driving the liquid crystal. Therefore, the color filter cannot be formed on the lower substrate 61, and the color filter 59 is formed on the upper substrate 62.
Also, APC has the property that it has not only high reflectance but also lower resistivity than ITO or the like, and is thus suitable as an electrode material and wiring material. Particularly, in comparison with ITO, APC has a resistivity of 3.9×10−6 Ωm, which is about 1/50 of the resistivity of 2×10−4 Ωm of ITO. Namely, with the same thickness, the width of APC wiring required for obtaining the same resistance value is 1/50 of the width of ITO wiring.
Therefore, in the liquid crystal device shown in FIG. 7 in which APC is used for lead wiring between electrodes and driver ICs, lead wiring can be made fine, as compared with the liquid crystal device shown in FIG. 6 in which ITO is used for lead wiring. Therefore, the area of a non-display area around an effective display area, i.e., a frame area, can be decreased, and thus the frame can be narrowed. Particularly, the liquid crystal device having the narrow frame can be contained in a restricted space in a casing of an electronic apparatus, and the quantity of information which can be displayed can be increased relative to the area of the liquid crystal device contained in the electronic apparatus. Therefore, the liquid crystal device is suitable for use for portable small electronic apparatus such as cell phones or the like.
However, in the conventional liquid crystal device shown in FIG. 7, APC constituting the segment electrode 67 and lead wiring causes electromigration in repeated use, possibly causing the defect that the electrode and wiring are narrowed or broken according to circumstances. There is thus the problem of low reliability.
In order to solve the problem, the applicant proposed a liquid crystal device having the construction shown in FIGS. 8 and 9, which has not been known yet. In these figures, the same members as those of the liquid crystal device 60 shown in FIG. 7 are denoted by the same reference numerals, and a description of these members is omitted. In the liquid crystal device shown in FIGS. 8 and 9, all the upper and side surfaces of the APC film 65, which constitutes the segment electrode 67, are coated with the ITO film 66. Also, all the upper and side surfaces of an APC film 54, which constitutes wiring 55, are coated with an ITO film 53. In FIGS. 8 and 9, reference numeral 52 denotes a black mask, and reference numeral 51 denotes a light shielding layer formed in the periphery of the display area.
As described above, when all the surfaces of the APC film are coated with the ITO film, the occurrence of electromigration in APC can be prevented even when the electrodes and wiring are formed by using APC, thereby forming a transflective liquid crystal device having high reliability.
In the above-described liquid crystal device, an aperture, i.e., a slit 64, is provided corresponding to each display dot in the internal region of the reflecting film 65 formed on the back-side substrate 61 shown in FIG. 9, and the illumination device 83 is disposed on the back of the liquid crystal device. In this construction, light emitted from the illumination device 83 is incident on the back-side substrate 61, transmitted through the slits 64 provided in the reflecting film 65, and then emitted from the observation side to realize a transmissive display.
In the liquid crystal device, in some cases, the ratio of the area of the region in which light is reflected for a reflective display to the area of the region in which light is transmitted for a transmissive display deviates from a desired ratio, i.e., a design ratio, due to errors produced in various steps such as that of forming the reflecting layer 65, that of bonding a pair of substrates 61 and 62 together, etc. For example, when the area of the light transmitting region is smaller than the desired area, and the area of the light reflecting region is larger than the desired area, the brightness of a transmissive display is lower than that in a reflective display. There is thus the problem of causing variations in display quality according to the display system.
The present invention has been achieved in consideration of the above problem, and an object of the present invention is to suppress the occurrence of variations in the area ratio of the light transmitting region to the light reflecting region of a transflective film even when various errors occur in manufacturing a liquid crystal device, thereby preventing the occurrence of variations in display quality even when the display system of the liquid crystal device is changed.